Plasma discharges can be used to excite gases to produce reactive gas containing ions, free radicals, atoms and molecules. Reactive gases are used for numerous industrial and scientific applications including processing solid materials such as semiconductor wafers, powders, and other gases.
One example of a reactive gas is atomic fluorine, which can be used to clean chemical vapor deposition (CVD) chambers for deposition of thin films onto substrate surfaces. CVD chambers need to be routinely cleaned to remove the deposits that build up on the surfaces of chamber parts other than the substrate surfaces. Wet cleaning of a chamber is labor intensive and hazardous to workers, while cleaning the chamber with atomic fluorine generated by a plasma source allows the deposits to be removed without opening the chamber to atmosphere, improving tool productivity and working conditions. Typical source gases for atomic fluorine include perfluorocompounds (PFCs) such as NF3, CF4, CHF3, C2F6, and C4F8.
Another example of a reactive gas is atomic oxygen, which can be used for photoresist removal in microelectronics fabrication. After pattern generation, photoresist is removed by exposing the wafer surface to atomic oxygen generated by a plasma source. Atomic oxygen reacts rapidly and selectively with photoresist, allowing the process to be conducted in a vacuum and at relatively low temperature.